That would be using a chisel to get the pully off the peice of rusted metal so that you can create a gap in order to get the removal tool behind the pully and over the screws. You need to loosen the 4 bolts, then pull out the pully, then get the tool behind there.
I used a long flat screwdriver and a hammer, started from underneath my truck and then finished off from the top. Finally the pully broke free from the rust.
I'll provide pics real soon